Optical adjustment of working range and beam spot size in electro-optical readers

ABSTRACT

Working range and laser beam cross-section are adjusted in an electro-optical reader for reading indicia by applying control voltages to a pair of variable lenses to change the shape of a liquid therein. An aperture stop maintains a constant beam cross-section as an input to one of the lenses.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/798,498, filed Mar. 11, 2004 now U.S. Pat. No. 7,201,318,and commonly assigned therewith.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to electro-optical systems forreading indicia, for example, bar code symbols, having parts withdifferent light reflectivities and, in particular, to an arrangementfor, and a method of, adjusting the working range and/or the laser beamcross-section for increased performance in the system.

2. Description of the Related Art

Various electro-optical readers and systems have previously beendeveloped for reading bar code symbols appearing on a label, or on asurface of a target. The bar code symbol itself is a coded pattern ofindicia. Generally, the readers electro-optically transform graphicindicia of the symbols into electrical signals which are decoded intoalphanumeric characters. The resulting characters describe the targetand/or some characteristic of the target with which the symbol isassociated. Such characters typically comprise input data to a dataprocessing system for applications in point-of-sale processing,inventory control, article tracking and the like.

The specific arrangement of symbol elements, e.g., bars and spaces, in asymbol defines the characters represented according to a set of rulesand definitions specified by a code or symbology. The relative size ofthe bars and spaces is determined by the type of code used, as is theactual size of the bars and spaces.

To encode a desired sequence of characters, a collection of elementarrangements is concatenated to form the complete symbol, with eachcharacter being represented by its own corresponding group of elements.In some symbologies, a unique “start” and “stop” character is used toindicate where the symbol begins and ends. A number of different barcode symbologies presently exists. The symbologies includeone-dimensional codes such as UPC/EAN, Code 39, Code 128, Codabar, andInterleaved 2 of 5.

In order to increase the amount of data that can be represented orstored on a given amount of symbol surface area, several new symbologieshave been developed. One new code standard, Code 49, introduced atwo-dimensional concept of stacking rows of elements vertically insteadof extending elements horizontally. That is, there are several rows ofbar and space patterns, instead of one long row. The structure of Code49 is described in U.S. Pat. No. 4,794,239. Another two-dimensional codestructure known as PDF417 is described in U.S. Pat. No. 5,304,786.

Electro-optical readers have been disclosed, for example, in U.S. Pat.No. 4,251,798; U.S. Pat. No. 4,369,361; U.S. Pat. No. 4,387,297; U.S.Pat. No. 4,409,470, U.S. Pat. No. 4,760,248 and U.S. Pat. No. 4,896,026,all of which have been assigned to the assignee of the presentinvention. These readers generally include a light source consisting ofa gas laser or semiconductor laser for emitting a light beam. The use ofsemiconductor devices as the light source in readers is especiallydesirable because of their small size, low cost and low powerrequirements. The laser beam is optically modified, typically by afocusing optical assembly, to form a beam spot having a certain size ata predetermined target location. The cross-section of the beam spot atthe target location may approximate the minimum width between symbolregions of different light reflectivity, i.e., the bars and spaces, butthe spot cross-section can be larger and, in some cases, more than twicethe minimum width.

In conventional readers, the light beam is directed by a scan componentalong a light path toward a target symbol. The reader operates byrepetitively scanning the light beam in a scan pattern, for example, aline or a series of lines across the target symbol by movement of thescan component such as a mirror disposed in the path of the light beam.The scan component may sweep the beam spot across the symbol, trace ascan line across and beyond the boundaries of the symbol, and/or scan apredetermined field of view.

Readers also include a sensor or photodetector which functions to detectlight reflected or scattered from the symbol. The photodetector orsensor is positioned in the reader in an optical path so that it has afield of view which extends at least across and slightly beyond theboundaries of the symbol. A portion of the light beam reflected from thesymbol is detected and converted into an analog electrical signal. Adigitizer digitizes the analog signal. The digitized signal from thedigitizer is then decoded, based upon the specific symbology used forthe symbol.

The scan pattern that scans the symbol can take a variety of forms, suchas repeated line scan, standard raster scan, jittered raster scan,fishbone, petal, etc. These beam patterns are generated by controlledmotions of the scan component in the beam path. Typically, the scancomponent is driven by some form of scanning motor to periodicallydeflect the beam through the desired beam scanning pattern. For arepeated line scan beam pattern, a polygonal mirror unidirectionallyrotated by a simple motor can be utilized. For more complex beampatterns, more involved drive mechanisms are required.

The frequency at which the beam pattern is executed is also an importantconsideration. The more times a symbol can be scanned in a given timeperiod, the chances of obtaining a valid read of the symbol areincreased. This is particularly important when the symbols are borne bymoving objects, such as packages traveling on a conveyor belt.

Symbols can also be read by employing imaging devices. For example, animage sensor device may be employed which has a two-dimensional array ofcells or photosensors which correspond to image elements or pixels in afield of view of the device. Such an image sensor device may include atwo-dimensional or area charge coupled device (CCD) or complementarymetal oxide semiconductor (CMOS) device and associated circuits forproducing electronic signals corresponding to a two-dimensional array ofpixel information for a field of view.

It is therefore known to use a CCD for capturing a monochrome image of abarcode symbol to be read as, for example, disclosed in U.S. Pat. No.5,703,349. It is also known to use a CCD with multiple buried channelsfor capturing a full color image of a target as, for example, disclosedin U.S. Pat. No. 4,613,895.

Many applications call for a hand-held reader in which the moving laserbeam device or the imaging device is accommodated. For suchapplications, the arrangement of electro-optical components must becompact in order to be accommodated in a hand-held package which may bepistol-shaped. Moreover, such readers must be lightweight andstructurally robust to withstand physical shock resulting from roughhandling. It is also desirable that minimal power be consumed duringoperation to extend battery life.

It is further desirable that the symbol be capable of being read over anextended range of working distances relative to the hand-held reader. Inthe case of a moving laser beam device, it is conventional to move oneor more lenses in the focusing optical assembly and, in turn, to movethe focus of the laser beam between a near position close to the readerand a far position further away from the reader. The lens movement istypically performed mechanically. This is disadvantageous for severalreasons. First, the mechanical movement generates vibrations which arepropagated through the reader to the user's hand, and may also generatedust to obscure the optics. Moreover, depending on the scan rate, thevibrations can generate objectionable, annoying, audible hum. Inaddition, the lens movement requires a drive which, in turn, consumeselectrical power, is expensive and slow, can be unreliable, occupiesspace and increases the overall weight, size and complexity of thereader.

It is generally known that a liquid crystal lens has been proposed toadjust the focus of an optical assembly. U.S. Pat. No. 5,305,731describes a liquid lens with an adjustable focal length. U.S. Pat. No.5,625,496 describes changing the index of refraction inside a liquidlens. French Publication No. 2,791,439 and No. 2,769,375 (and itsequivalent, U.S. Pat. No. 6,369,954) describe a variable focus liquidlens.

SUMMARY OF THE INVENTION Objects of the Invention

One object of this invention is to provide an improved arrangement forand method of adjusting the working range and/or beam spot size of areader for reading a data-encoded symbol.

Another object of this invention is to provide an arrangement which iscompact, lightweight, durable and efficient in construction and quietand reliable in operation, and thus is ideally suited for portablehand-held applications.

Still another object of this invention is to adjust focal length in anelectro-optical reader and/or change the beam spot cross-section withoutmechanically moving lenses.

FEATURES OF THE INVENTION

In keeping with these objects and others which will become apparenthereinafter, one feature of this invention resides, briefly stated, inan arrangement for, and a method of, electro-optically reading indicia,such as one- and/or two-dimensional bar code symbols.

The invention provides a pair of variable optical lenses, preferablyeach having a pair of light-transmissive liquids arranged along anoptical path, the liquids of each lens being immiscible, of differentoptical indicies of refraction, and of substantially the same density.One of the liquids has a shape in a rest state for optically modifyinglight passing through the one liquid along the optical path toward theindicia to have a first optical characteristic. In accordance with thisinvention, a controller is operative for applying a voltage across theone liquid of each lens to change the shape thereof, and for opticallymodifying the light to have a second different optical characteristic.

In the case of a moving beam reader, a light source such as a laserdiode emits the light as a laser beam, and the changing of the shape ofthe one liquid of a first one of the lenses focuses the laser beam atone of the working distances relative to the first variable lens alongthe optical path, and the changing of the shape of the one liquid of asecond one of the lenses optically modifies the light to have a selectedcross-section at the one working distance.

The controller applies a periodic voltage across the one liquid of eachlens, either continuously during the reading, or only after determiningthat a particular indicium or bar code symbol has not been successfullyread.

Each variable lens may include a single fixed lens, or a pair of fixedlenses at opposite ends thereof. The one liquid may be radiallysymmetrical with the optical path in the rest state, or in amodification, may extend along a transverse axis perpendicular to theoptical path and modify the cross-section of the laser beam. Anelliptical beam cross-section is preferred for reading one-dimensionalsymbols, whereas a circular beam cross-section is preferred for readingtwo-dimensional symbols. Changing the beam cross-section enables thereader to adaptively read damaged or poorly printed symbols.

An aperture stop in the optical path is operative for maintaining aconstant beam cross-section as an input to the first variable lens.

The changing between different focal planes and/or the changing of thebeam cross-section is performed without mechanically or physicallymoving solid lenses, thereby decreasing the noise and vibration and dustin such readers, as well as the size, weight, power and volumerequirements. The variable liquid lens will not wear out over time.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a hand-held reader for reading a barcode symbol in accordance with the prior art;

FIG. 2 is a cross-sectional view of a variable lens for use in thehand-held reader of FIG. 1;

FIG. 3 is a diagrammatic view of an arrangement using the variable lensof FIG. 2 for use in the reader of FIG. 1;

FIG. 4 is a diagrammatic view of an arrangement using the variable lensfor use with an imaging reader;

FIG. 5 is a broken-away view of a part of a variable lens in accordancewith a modification;

FIGS. 6, 7 and 8 are respective views of beam cross-sections produced bythe variable lens of FIG. 5; and

FIG. 9 is a diagrammatic view using two variable lenses and an aperturestop for use in the reader of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference numeral 20 in FIG. 1 generally identifies a hand-held readerfor electro-optically reading indicia, such as bar code symbol 24,located in a range of working distances therefrom. The reader 20 has apistol grip handle 21 and a manually actuatable trigger 22 which, whendepressed, enables a light beam 23 to be directed at the symbol 24. Thereader 20 includes a housing 25 in which a light source 26, a lightdetector 27, signal processing circuitry 28, and a battery pack 29 areaccommodated. A light-transmissive window 30 at a front of the housingenables the light beam 23 to exit the housing, and allows light 31scattered off the symbol to enter the housing. A keyboard 32 and adisplay 33 may advantageously be provided on a top wall of the housingfor ready access thereto.

In use, an operator holding the handle 21 aims the housing at the symboland depresses the trigger. The light source 26 emits a light beam whichis optically modified and focused by an optical focusing assembly 35 toform a beam spot on the symbol 24. The beam passes through a beamsplitter 34 to a scan mirror 36 which is repetitively oscillated at ascan rate of at least 20 scans a second by a motor drive 38. The scanmirror 36 reflects the beam incident thereon to the symbol 24 and sweepsthe beam spot across the symbol in a scan pattern. The scan pattern canbe a line extending lengthwise along the symbol along a scan direction,or a series of lines arranged along mutually orthogonal directions, oran omnidirectional pattern, just to name a few possibilities.

The reflected light 31 has a variable intensity over the scan patternand passes through the window 30 onto the scan mirror 36 where it isreflected onto the splitter 34 and, in turn, reflected to thephotodetector 27 for conversion to an analog electrical signal. As knownin the art, the signal processing circuitry 28 digitizes and decodes thesignal to extract the data encoded in the symbol.

In accordance with this invention, the focusing optical assembly 35 isconfigured as a variable lens as shown in FIG. 2. The variable lens hasa housing 40 in which a first liquid 42, shown in droplet form, and asecond liquid 44 are arranged along an optical path 46 which, asdescribed below in connection with FIGS. 3-4, extends toward an indiciasuch as bar code symbol 24 to be read by an electro-optical reader 20.

The liquids 42, 44 are light-transmissive, immiscible, of differentoptical indicies of refraction and of substantially the same density.The liquid or drop 42 is constituted of an electrically insulatingsubstance. For example, an oil, an alcane, or a blend of alcanes,preferably halogenated, or any other insulating liquid may be used forthe drop 42. The liquid 44 is constituted of an electrically conductivesubstance, for example, water loaded with salts (mineral or other), orany other liquid, organic or not, and preferably made conductive by theaddition of ionic components.

The housing 40 is constituted of an electrically insulating,light-transmissive, material, such as glass, preferably treated withsilane or coated with a fluorinated polymer, or a laminate offluorinated polymer, epoxy resin and polyethylene. The housing 40includes a dielectric wall 48, preferably having a well 50 in which thedrop 42 is accommodated in symmetrical relation relative to the opticalpath or axis 46. The wall 48 normally has a low wetting characteristiccompared to the drop 42, but a surface treatment insures a high wettingcharacteristic and maintains a centered position of the drop 42 andprevents the drop from spreading. The well 50 further helps to preventsuch spreading.

A first electrode 54 extends into the liquid 44, and a second electrode52 is located below the wall 52. The electrodes are connected to avoltage source V. The electrodes, especially electrode 52, arepreferably light-transmissive. As explained in U.S. Pat. No. 6,369,954,the entire contents of which are incorporated herein by referencethereto, when a voltage is applied across the electrodes, an electricalfield is created which alters the wetting characteristic of the wall 48with respect to the drop 42. The wetting increases substantially in thepresence of an electrical field.

With no voltage applied, the drop 42 takes the generally hemisphericalshape shown in solid lines in FIG. 2, and its outer surface “A” isconvex. When a voltage is applied, the wetting of the dielectric wall 48increases, and the drop 42 deforms and takes the shape shown in dashedlines in FIG. 2, and its outer surface “B” is more convex with a smallerradius of curvature. This deformation of the drop changes the focus ofthe lens 35 and is employed by the present invention to read the symbol24 over an extended range of working distances, as described below inconnection with FIGS. 3-4.

By way of example, the drop 42 in the rest state has a diameter of about6 mm. If the liquid 44 is salt water, its index of refraction is about1.35. If the drop 42 is oil, its index of refraction is about 1.45.About 40 diopters of focus variation can be achieved for an appliedvoltage of about 40v RMS. The response time of the lens is severalhundredths of a second, in which case, if a periodic voltage is used,the frequency can be between 50 Hz and 10 kHz so that its period issmaller than the response time.

Turning to FIG. 3, the light source 26 of FIG. 1 is shown as a laserdiode. The scan mirror 36 and its drive 38 are likewise depicted in FIG.3. The change in curvature of the drop 42 in the variable lens 35 isresponsible for varying the focal point between close-in position Z1 andfar-out position Z2. The symbol 24 can be read at, and anywhere between,these end-limiting positions, thereby improving the working range of thereader.

The voltage is preferably periodic, preferably a square wave drivevoltage. The square wave is easily created with a variable duty cycle bya microprocessor 60 having a built-in pulse width modulator circuit. Thedrive voltage could also be sinusoidal or a triangular wave signal, inwhich case, the amplitude of the voltage controls the shape of the drop42 and, in turn, the focal length and the working distance. The squarewave does not require a voltage as high as a sinusoidal wave for a givenchange in focal length. For example, many readers use a single 5 voltpower supply. The variable lens requires much more than 5 volts and,hence, a higher voltage must be generated within the reader to drive thevariable lens. The lower this generated voltage needs to be, the lowerthe cost of the voltage generation circuitry.

When a square wave is used, focal length changes are achieved by varyingthe duty cycle. When a sinusoidal wave is used, focal length changes areobtained by varying the drive voltage amplitude. The amplitude or theduty cycle can be changed in discrete steps (digital manner) orcontinuously (analog manner) by the micropressor or controller 60,preferably mounted on the same circuit board as the signal processingcircuitry 28. The voltage could also be a constant DC voltage.

In the arrangement of FIG. 3, during reading, the laser beam is beingscanned by the scan mirror 36 across focal planes generally transverselyof the optical path or axis 46. The controller 60 may operate to applythe periodic voltage to the variable lens 35 at all times, or atselected times. Thus, the voltage can be applied for each scan, or forevery other scan, etc. The voltage can be applied not only duringscanning, but even afterward. The voltage can be initiated at the pullof the trigger 22, or only after a symbol has been detected. The voltagecan be applied automatically, or only after a signal analyzer 62,preferably a microprocessor, has determined that the symbol beingscanned has not yet been successfully decoded and read.

FIG. 4 is analogous to FIG. 3, except that it depicts an imager having asensor 64, preferably a CCD or CMOS array having mutually orthogonalrows and columns of photocells for imaging the symbol located at, oranywhere between, the imaging planes Z3 and Z4, thereby providing theimager with an extended working range or depth of focus in which tocollect light from the symbol. As before, the change in shape of thedrop 42 when a periodic voltage is applied to the variable lens 35enables the extended depth of focus to be achieved.

As described so far, the change in curvature of the drop 42 is betweentwo convex curvatures A, B. It is also within the spirit of thisinvention to deform the drop between different curvatures. For example,it is possible that the outer surface of the drop could be a meniscus,that is concave in the rest state, generally flat to focus the light ata first focal plane when a first voltage is applied, and convex to focusthe light at a second focal plane when a second, different voltage isapplied.

Referring to FIG. 2, the variable lens 35 may also have a fixed convexlens 66 at one axial end region, and a fixed concave, or plano-concave,lens 68 at the opposite axial end region. These fixed lenses are part ofthe overall optical system and assist in minimizing any kind ofaberrations, for example, chromatic aberrations. The optical systemshould advantageously include an aperture stop (not illustrated) whichcan be positioned anywhere in the optical path.

In a variant, the drop 42 need not have a generally hemispherical shape,that is radially symmetrical relative to the optical path 46, but could,as shown in FIG. 5, be elongated along a transverse direction generallyperpendicular to the optical path. The cylindrical drop, now identifiedby reference numeral 70, rests in a channel-shaped well 72 formed by adielectric wall 74.

Upon application of a periodic voltage, the cylindrical drop 70, nowacting as a cylindrical lens, changes the cross-section of the laserbeam passing therethrough en route to the symbol. Thus, the beamcross-section 76 from a laser diode is generally elliptical as shown inFIG. 7. The illustrated x-axis is along the scan direction. The y-axisextends lengthwise of the bars and spaces of the symbol.

For one-dimensional symbols, a more elliptical or elongated beamcross-section 78, such as the one shown in FIG. 6, is desired. Fortwo-dimensional symbols, a more circular beam cross-section 80, such asdepicted in FIG. 8, is desired. By applying a periodic voltage, thecylindrical drop 70 can optically modify the cross-section of the beamto be either cross-section 78 or 80, or any shape in between. Theseshape changes can occur continuously or in stepwise manner and areespecially useful in reading damaged or poorly printed symbols, therebyimproving system performance.

It will be seen that the change in focus and/or the change in beamcross-section is accomplished without mechanical motion of any solidlenses. Except for the liquids, all parts of the variable lens 35 can bemade of molded materials.

This invention proposes using more than one variable lens in the opticalpath. One variable lens can be used for focus variation, another can beused to change the ellipticity of the beam cross-section and/or themagnification (i.e., the zoom effect). Multiple lenses can also be usedto reduce astigmatism similar to a Petzval lens.

More specifically, as shown in FIG. 9, two variable lenses are arrangedin series along the optical path. An aperture stop 82 is advantageouslypositioned between the laser diode 26 and the first variable lens. Thecontroller 60 has two outputs, one for each variable lens. Otherwise,the same reference numerals as were used above in connection with FIG. 3have been used to identify like parts.

The aperture stop is operative to maintain a constant beam diameter asan input to the dual lens system of FIG. 9, or the single lens systemsof FIG. 3 or 4, thereby assuring consistency with laser beam divergencevariations.

As described above in connection with FIG. 3, varying the focal lengthwill cause the beam spot or waist, i.e., the point where the laser beamhas a minimum diameter in cross-section, to be moved between thedifferent working range positions Z1 and Z2. When the focal length isvaried, the size of the waist will change also. As the focal length isadjusted to move the waist outwards toward Z2, the waist increases indiameter, and when the waist is moved inwards toward Z1, the waistshrinks in diameter. As a result, resolution decreases as the waist ismoved outwards, thereby resulting in a limitation in the capability ofthe reader to read high density symbols at far-out distances.

On the other hand, it is sometimes desirable to scan with a large sizedwaist at close-in distances, especially for reading damaged or lowcontrast symbols, because the large waist reduces speckle noise andreduces resolution making it easier for the reader to ignore printingdefects.

The dual lens system of FIG. 9 enables the first variable lens to changethe diameter of the waist where it is incident on the second variablelens. By controlling the waist diameter on the second lens, it ispossible to maintain a constant waist size as the waist location ischanged. The constant waist size can be large if desired for reading lowdensity, damaged or low contrast symbols, or can be small for readinghigh density symbols over an extended range. The dual lens system canposition any beam waist size at any working range distance as may benecessary for any scanning application.

The focal lengths of the two lenses can be controlled by the signalanalyzer or microprocessor 62, either independently or simultaneously,in a coordinated manner to produce the desired waist size at the desiredworking distance. The waist size and/or working distance can be pre-setto optimize the reader for specific applications, or can be controlledby the microprocessor 62 running algorithms that analyze the returnsignal from the symbol and make adjustments as necessary to optimize thecapability of the reader to read the symbol being scanned.

Advantageously, the same microprocessor used to decode the symbol isused as the signal analyzer. Moreover, the same microprocessor can beused to communicate the decoded data to a remote host computer via ahard-wired or wireless link, e.g., radio frequency or infrared.

Other types of variable lenses, other than the liquid lenses describedherein, could also be employed.

This invention further contemplates using multiple electrodes in thevariable lens to change the curvature of the drop 42 in differentdirections, thereby transforming a spherical lens to a cylindrical lens,for example. The minimum cross-section of the beam, also known as thebeam waist, can be changed and, at the same time, the ellipticity of thebeam can be changed. The use of additional (more than two) electrodesmay be used to correct some specific aberration if needed, not only fora moving beam reader, but also for an imager.

In a moving beam scanner, not only can the variable lens be employed inthe outgoing path toward the indicia to be read, but also the variablelens may be employed in the return path along which the reflected lightreturns to a photodetector. The variable lens may be positioned in frontof the photodetector to control optical automatic gain by changing theamount of the reflected light impinging on the photodetector.

It will be understood that each of the elements described above, or twoor more together, also may find a useful application in other types ofconstructions differing from the types described above.

While the invention has been illustrated and described as embodied inelectro-optical readers, it is not intended to be limited to the detailsshown, since various modifications and structural changes may be madewithout departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

1. An arrangement for electro-optically reading indicia having parts ofdifferent light reflectivity, comprising: a) a plurality of variablefocus optical lenses spaced apart along an optical path each lens havinga pair of light-transmissive liquids arranged along the optical path,the liquids of each lens being immiscible, of different optical indiciesof refraction, and of substantially same density, one of the liquids ofeach lens having a drop shape accommodated in a well in a rest state foroptically modifying the light beam passing through said one liquid alongthe optical path toward the indicia to have a first opticalcharacteristic; b) a light source for generating a light beam with across-section, and for directing the light beam along the optical paththrough the lenses toward the indicia located within a range of workingdistances away from the light source; and c) a controller forcontrolling one of lenses to focus the light beam at one of the workingdistances at which the indicia is located, and for controlling the otherof the lenses to optically modify the light beam to have a selectedcross-section at said one working distance, the controller beingoperative for applying a voltage across said one liquid of each lens tochange the shape thereof, and for optically modifying the light beam tohave a second different optical characteristic.
 2. The arrangement ofclaim 1, and an aperture stop in the optical path between the lightsource and said one lens, for forming a constant beam cross-section forthe light beam prior to passing through said one lens.
 3. Thearrangement of claim 1, wherein said one liquid is electricallyinsulating, and wherein the other of the liquids of each lens iselectrically conductive, and wherein a first electrode is disposed atone side of said one liquid, and wherein a second electrode is immersedin said other liquid at an opposite side of said one liquid, and whereinthe voltage is applied across the electrodes of each lens.
 4. Thearrangement of claim 1, wherein each variable lens includes at least onefixed focal lens spaced apart from the liquids along the optical path.5. The arrangement of claim 4, wherein there are two fixed focal lenseshaving positive and negative optical powers respectively, and whereinthe two fixed focal lenses are located at opposite ends of each variablelens.
 6. The arrangement of claim 1, wherein the first and secondoptical characteristics of said one lens are different focal planesspaced apart along the optical path at different working distancesrelative to the light source.
 7. The arrangement of claim 1, wherein thefirst and second optical characteristics of said other lens aredifferent sizes of the cross-section of the light beam.
 8. Thearrangement of claim 1; and a scanner for scanning at least one of thelight beam, and a field of view, over the indicia.
 9. The arrangement ofclaim 8, wherein the controller is operative for continuously applyingthe voltage as a periodic voltage during scanning.
 10. The arrangementof claim 8, wherein the controller is operative for determining whetherthe indicia was successfully scanned and read, and for applying thevoltage upon a determination that the indicia was not successfullyscanned and read.
 11. The arrangement of claim 10, wherein thecontroller is a microprocessor operative for decoding an electricalsignal derived from light reflected from the indicia.
 12. Thearrangement of claim 11, wherein the microprocessor is operative forcommunicating with a remote host.
 13. An arrangement forelectro-optically reading indicia having parts of different lightreflectivity, comprising: a) a light source for directing a light beamalong an optical path; b) an aperture stop for forming a constantcross-section for the light beam; c) a variable optical lens having apair of light-transmissive liquids arranged along the optical path, theliquids being immiscible, of different optical indicies of refraction,and of substantially same density, one of the liquids having a dropshape accommodated in a well in a rest state for optically modifying thelight beam of constant cross-section passing through said one liquidalong the optical path toward the indicia to have a first opticalcharacteristic; and d) a controller for applying a voltage across saidone liquid to change the shape thereof, and for optically modifying thelight beam to have a second different optical characteristic.
 14. Thearrangement of claim 13, wherein the first and second opticalcharacteristics are different focal planes spaced apart along theoptical path at different working distances relative to the variablelens.
 15. A method of electro-optically reading indicia having parts ofdifferent light reflectivity, comprising the steps of: a) spacing aplurality of variable focus optical lenses apart along an optical patheach lens having a pair of light-transmissive liquids arranged along theoptical path, the liquids of each lens being immiscible, of differentoptical indicies of refraction, and of substantially same density, oneof the liquids of each lens having a drop shape accommodated in a wellin a rest state for optically modifying the light beam passing throughsaid one liquid along the optical path toward the indicia to have afirst optical characteristic; b) generating a light beam with across-section, and directing the light beam along the optical paththrough the lenses toward the indicia located within a range of workingdistances away from the lenses; and c) controlling one of lenses tofocus the light beam at one of the working distances at which theindicia is located, and controlling the other of the lenses to opticallymodify the light beam to have a selected cross-section at said oneworking distance, by applying a voltage across said one liquid of eachlens to change the shape thereof, and for optically modifying the lightbeam to have a second different optical characteristic.
 16. The methodof claim 15, and inserting an aperture stop in the optical path, forforming a constant beam cross-section for the light beam prior topassage through said one lens.